ant-design/components/splitter/hooks/useResizable.ts

import * as React from 'react';

import type { ItemType } from './useItems';

export type ResizableInfo = {
  resizable: boolean;
  startCollapsible: boolean;
  endCollapsible: boolean;
};

export default function useResizable(items: ItemType[], pxSizes: number[]) {
  return React.useMemo(() => {
    const resizeInfos: ResizableInfo[] = [];

    for (let i = 0; i < items.length - 1; i += 1) {
      const prevItem = items[i];
      const nextItem = items[i + 1];
      const prevSize = pxSizes[i];
      const nextSize = pxSizes[i + 1];

      const {
        resizable: prevResizable = true,
        min: prevMin,
        collapsible: prevCollapsible,
      } = prevItem;
      const {
        resizable: nextResizable = true,
        min: nextMin,
        collapsible: nextCollapsible,
      } = nextItem;

      const mergedResizable =
        // Both need to be resizable
        prevResizable &&
        nextResizable &&
        // Prev is not collapsed and limit min size
        (prevSize !== 0 || !prevMin) &&
        // Next is not collapsed and limit min size
        (nextSize !== 0 || !nextMin);

      const startCollapsible =
        // Self is collapsible
        (prevCollapsible.end && prevSize > 0) ||
        // Collapsed and can be collapsed
        (nextCollapsible.start && nextSize === 0 && prevSize > 0);

      const endCollapsible =
        // Self is collapsible
        (nextCollapsible.start && nextSize > 0) ||
        // Collapsed and can be collapsed
        (prevCollapsible.end && prevSize === 0 && nextSize > 0);

      resizeInfos[i] = {
        resizable: mergedResizable,
        startCollapsible: !!startCollapsible,
        endCollapsible: !!endCollapsible,
      };
    }

    return resizeInfos;
  }, [pxSizes, items]);
}